The Garden of Eden
by Angelus Fortis
Summary: The angel Castiel goes back in time to save Dean from the Mark of Cain and stop the events that will inadvertently bring The Darkness into the world. He makes the sacrifice instead of the Winchester but what happens to an angel other than Lucifer when tainted with the darkest of evils? AU from Season 11, then Season 9 and onward.
1. Lock and Key

**A/N: I know I'm a terrible author, I just started this new fic and it's so complex my brain is about to burst. I have a lot of ideas for this one which is pretty good 'cause 'It's Us Against the World' kind of flopped and it's scheduled for re-write. I hope you guys won't hate me. But I've always been thinking of this plot twist ever since Dean had the Mark of Cain and when Chuck said about entrusting the Mark to Lucifer in the first place. So yeah, hope you guys read this and tell me if it's crap.**

 **P.S. I always wanted to do a time travel fic and so, hopefully, finish this one. Oh and sorry if Chuck is OOC, I never really wanted god to be so invested in the show. So this is my version of Chuck.  
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 **Disclaimer: Eric Kripke, the WB and CW own Supernatural. But do they own the moon? No?**

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Chapter Synopsis: _Chuck Shurley confronts Castiel after the Darkness attempts to send Dean a message. AU from 11x10 – The Devil in the Details._

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 **Chapter 1 - Lock and Key**

The only thing that Castiel felt at that moment was a displacement in the air, the familiar bursts of light and colors, and a constant vibration as he was transported somewhere between dimensions. Then in an instant, he was on solid ground again. He stumbled ungracefully, knocking down chairs and tables in the room. Cas panted, out of breath, then palmed at the burning sensation on his midsection, grunting at the wet feel of blood between his fingers. Amara's touch did no favors to his already depleted Grace.

Finally noticing that he was in unfamiliar territory, Castiel rolled then stood up from his sprawled position on the floor. He looked around and cautiously held his angel blade in front of him as he noticed something. There was a presence in the room he couldn't put his finger on - like an enigma. Nothing sinister but very, very powerful. He kept his guard up.

"Hello, Castiel."

Cas whipped his head around the establishment, for what he could see, it was deserted.

"Right here," the voice once again acknowledged him. The angel warily followed the source of the voice, clenching and unclenching his hand on the blade as he went. Castiel stopped on a lonely table, shoved in a corner and furthest from the rest. A familiar face with unruly dark hair popped out of the booth.

"Chuck Shurley?" Cas asked, surprised to see the former prophet after all these years. Chuck should be dead, if Kevin wasn't proof enough. He was bewildered to say the least, but the matter with Amara and the pain in his chest told him there were more pressing things than meeting the dead prophet in some unknown place. Unless, it was directly related to the Darkness. "Are we in Heaven?"

That was the most logical thing he could think of but Chuck shook his head, a proud smile on his face. "We're in a pocket dimension. One I personally made. It's totally safe here."

Castiel was passed the point of utter confusion and just didn't even understand the words the man was saying. Chuck gave him a sympathetic look and gestured towards the other seat directly facing him.

"Why don't you take a seat? We have a lot to talk about, my son."

Realization dawned on the angel. His trembling fingers slipped from the angel blade he was holding, emitting a clanging sound to reverberate in the vast space between them. He shuffled weakly, knees feeling like rusty joints and arms leaden. Castiel sat heavily across Chuck, an expression of awe and wonder on his battered face that belonged to a child finally meeting his long lost father.

And it was, his long lost heavenly father with the earthly visage of the prophet known as Chuck Shurley. Cas had given up on looking for him for a long time now. A father he never knew, never even met before. But now, knowing that Chuck was actually god and that he was there with the Winchesters and the angel during the Apocalypse, it was hard not to question why - why didn't he help them then?

He should've felt anger or something associated with it but all Cas could muster was a sad smile and a fat tear trailing down his cheek. He couldn't get mad at his father, no matter what he did or didn't do. He was god, after all and he resurrected Castiel for so many times now, it possibly meant he cared. He had found him, at last.

Chuck's brown eyes were filled with sadness as he touched Castiel's forehead, a bright light engulfed the angel's form, healing him. Cas blinked, then opened his dress shirt where blood and pain were present earlier but now only had an unblemished white patch of smooth skin on his chest. He looked inquisitively at Chuck.

"The Darkness carved a few words on you. I couldn't stand looking at it," his father shrugged, a deep seated frown on his face.

Cas didn't want to get his hopes up but hope was a traitorous thing, "Will you help us defeat her?" God sighed, crossing his arms and shooting Castiel a troubled look. The angel felt dread and disappointment warring inside him. This wasn't good. "You won't," he intoned hollowly.

"I won't," Chuck agreed. "Do you know why I left Heaven, Castiel?"

The angel didn't respond, only guilty blue eyes staring at his father. God didn't have to say it, Castiel and his brethren have done unspeakable things under his name and all because of some petty grab at Paradise. It wasn't a mystery now, really.

"I was disappointed in all of you." Hearing the exact words come from Chuck's mouth made him cringe. "I would've come back eventually, I just wanted to test your independence while I was away. And look where it got us. Your brothers and sisters have ruined Heaven and Earth."

The angel had the extreme urge to do penance and apologize. It was true, it was all true. The Heavenly Host had failed to do their real jobs. "I-I am sorry, Father," Castiel stuttered.

Chuck didn't seem to hear him. "Parenting is a hard job, son. Sometimes, you have to stay away from your children, watch them do mistakes and miracles. Letting them learn from their actions rather than teaching them a lesson. Loosen the reigns in a bit, you know. Sometimes, it looks cruel. Everyone thinks I've abandoned them but I've always been everywhere, nudging people there, helping people here. Life is unfair for anyone, Castiel, and that's what makes living fair for everybody. Do you understand me?"

Cas tentatively nodded his head. He didn't understand everything but he thought he understood the most important parts. "Angels, demons and humans alike." God smiled at him then, and the angel felt nothing could make him happier than his own father's affections directed at him.

"I'm proud of you, Castiel." Cas' felt his heart stutter a bit and his breathing cut short. "You're the only one who understood, who loved the humans unconditionally. You accepted free will with open arms. You _are_ a good angel. Remember that."

Castiel couldn't believe what he was hearing. God, his father was proud of him. He didn't know what to say to that but he gulped down the lump forming in his throat and rasped a heartfelt, "Thank you."

Chuck nodded, gracing him with a small smile but then the levity was off from his face, brows furrowing. "And yet, I can't help you defeat the Darkness. Believe me, I want to," he amended to the open-mouthed angel. "The thing is, we don't have enough firepower to do it, and if we had, we shouldn't kill her."

"Why not?"

His father raised an incredulous eyebrow, "Except from the part where nobody isn't supposed to kill anybody?" Okay, now Castiel was just downright guilty. Who knew how much blood was spilled by his hands already (Chuck probably did) and he was once again willing to sacrifice an entity - his father's sister - for the sake of everything. It sounded like fair price to him but maybe the means never really justified the end.

"She's my sister and I just want her locked away, not killed. Then there's the issue of maintaining the cosmic balance of the universe. Y'know, Darkness and Light? Night and Day?..."

"Yin and Yang?" Offered the angel.

Chuck clapped his hands together, producing bright sparks."Exactly!" He looked Castiel in the eye, "So if the Darkness goes poof, every form of reality goes poof. It's that simple."

Castiel mulled over what god was saying, which was absolutely no help for their current predicament at all. They couldn't - shoudn't - kill Amara but can they lock her away this time? Chuck seemed to pick up on his train of thought. His father cleared his throat, bringing Cas' attention to him.

"I needed three archangels and myself to lock my sister away using the Mark. Right now, Michael and Lucifer are in the Cage and Gabriel's... out of the game. There just isn't enough time or power to do it again."

"Then are we doomed?" Because even if the Darkness wasn't killed, she'd destroy everything in creation anyway.

Chuck sighed for the second time during their whole conversation, "Always have faith, Castiel. I've found a solution but... well, the stakes are high and a sacrifice is desperately needed." Cas found himself on the edge of his seat, impatiently waiting for what Chuck had to say.

"The Mark's the only thing that tethered her to her prison and now it's gone. Dean had it recently, then Cain and lastly, Lucifer. So what triggered this problem is that the Mark never stayed in one place. It was passed on and so the risk of getting rid of the Mark from each other was highly possible. Like you know, how Dean was able to kill Cain in the first place."

Castiel never thought of the consequences when those things happened, especially when Dean possessed the Mark of Cain himself. He should've known nothing good would come from blindly running towards their enemies. "Now, no one's holding the Mark, except from Amara. So how?"

"Well, we need another person to carry the Mark of course."

"Time travel," Castiel thought out loud, making Chuck grin.

"Bingo! Time is pretty relative, so if we went back in time and stayed there for too long, she'll notice something and we're dead. But if we went back in time before the Mark was transferred to Dean, not only will the balance of past and future remain, but the Darkness wouldn't be able to come out in the first place."

Yes, this plan did make perfect sense for the angel and it seemed like the only sensible thing to do rather than kill the Darkness and end the world. But there was also the issue of the 'sacrifice' Chuck was talking about. Was it possible that his father was asking him to save them all? Castiel knew he was so broken inside, little bout of harsh memories would make him tremble. Even now, he was still feeling the side effects of Rowena's spell and he didn't know how much time he had left until he was a shaking pathetic mess on the floor. But if this was the only thing that could save Sam and Dean and the whole world, he was prepared to do it.

Chuck slumped on his seat and pinched the bridge of his nose in weariness, "I've sometimes thought those two idiots didn't deserve such love and loyalty from you, but they're your family too, aren't they, Castiel?" Cas nodded quietly. "But I'm not ordering you of anything, my son. You have to want this. I made free will for a reason."

"You know my answer, Father," Castiel replied, meeting Chuck's eyes with his determined blue ones. If this is his penance, he would gladly receive it. Anything to make his father proud and save the ones he love. It was a fair sacrifice.

God made a noise of agreement, "I'm going to restore your Grace and more, but I won't be able to make you into an archangel. It's messy business and time we don't have. We need you to be at full power, Castiel. The Mark is a curse that taints a person of his own darkness. A more evil and twisted version of it. As a powerful angel, the effects will be less than gradual but…"

"But I'll become like Lucifer himself." He knew it would come down to that eventually but even so, he wasn't changing his mind about the plan.

Chuck's expression looked pained. He leaned nearer towards Castiel and rested a hand on his shoulder, searching something in the angel's face. "Remember my son, the balance must remain."

Before Castiel could get a word in, his father was standing over him and snapping his fingers. The world was once again bombarded with light and colors and his metaphysical body traveling through impossible speeds. He landed somewhere then, stumbling a little as his surroundings stopped spinning. Cas bumped into something tall and the thing made an indignant sound of surprise.

"Cas? Are you alright?" He swiveled his head to a worried looking Sam Winchester. The hunter was holding a nasty looking syringe and a Men of Letters book in another hand. Castiel remembered this, it was the time when he extracted the resonating Grace left by Gadreel. And this meant he had truly, successfully gone back in time.

The angel looked up at Sam, an apology already at the tip of his tongue. "I'm sorry, Sam. I need to save Dean." Castiel didn't even think, never even noticed the knowledge and Grace inside him as he stretched his new wings, back to its former glory, and flying off to where Crowley and Dean were talking with the Father of Murder. He disappeared from the visible spectrum, leaving a confused and startled younger Winchester inside the Bunker.

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 **Hope it wasn't total craziness, anyway please do review. Reviews are my lifeblood. Also please Fav and Follow! This is a complex plot so the updates might come in slowly.  
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	2. Dancing with Demons

**A/N: Oh my CHUCK! Thank you so much for the reviews, guys. It's awesome that you think my idea is awesome so, here's chapter 2 and it's... idk, you decide how it is. Sorry if it isn't long enough. Sadly, I had a bit of a struggle writing the ending and my mum nattering in the background didn't help matters *sigh* Anyway please read and let me know what you think!**

 **P.S. First part of the conversation between Cain and Dean is Canon.**

 **Disclaimer: Roses are red, violets are blue, if you're a fan then I'm a fan too! Eric Kripke, the WB and CW own Supernatural. Oh but I'm obsessed so I'll play it natural.  
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Chapter Synopsis: _Cain is interrupted in the middle of transferring the Mark when a disheveled looking Castiel appears between them. Dean is not amused, Crowley runs away with his tail between his legs. AU from 09x11 – First Born._

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 **Chapter 2 – Dancing With Demons**

Dean was getting irritated by the second. The King of Hell breathing down his neck and a swarm of bloodthirsty demons eager to rip them all to pieces outside weren't helping the situation either. He paced around Cain's kitchen, grumbling under his breath and adrenaline making him want to punch something. Preferably Crowley's face... or Abaddon's, whichever came at him first. He looked around for a moment and was relieved to see Cain coming back from whatever hellhole he went to.

"What the hell, man? You in or out? I'm getting head spins," Dean demanded.

The demon ignored his brashness, wanting nothing more than to change the subject and give the Winchester what he needed. "I can give you the Mark, Dean. If that's what you truly want."

Mark? What mark? Did Cain mean the blood red thing on his arm? Whatever, Dean wasn't up for games right now and he thought the Father of Murder was just being annoyingly cryptic. He scowled at him, "What are you talking about?"

"The Mark can be transferred to someone who's worthy."

A beat, then, "You mean a killer like you?"

"Yes."

Dean didn't know how to react to that. Should he feel bad about it? Maybe insulted? "Can I use it to kill the bitch?"

"Yes. But you have to know, with the Mark comes a great burden. Some would call it a great cost."

"Yeah, well, spare me the warning label. You had me at 'kill the bitch'." There wasn't enough time to mull things over so as usual, Dean used the Winchester way to decide things - rush in blindly.

Cain sighed. Dean wasn't thinking straight but if he really did had a chance to kill the Knight of Hell, maybe Cain had his _own_ chance at revenge... So be it.

May Fate have mercy on Dean Winchester. "Good luck, Dean. You're gonna need it."

"Yeah, I get it a lot. Let's dance."

Dean was just finished saying the last word in when the air suddenly rippled, crackling with electricity. There was the familiar fluttering of wings. The occupants of the room turned their heads to look at the source - a disheveled looking Castiel. The angel hurriedly took stock of the situation, eyes immediately scanning the smooth unblemished skin of Dean's arm. There was a flash of relief, then determination and finally rage on his face. Before the Winchester could spit out a stunned 'Cas?', Castiel was touching his shoulder and transported him inside the safety of the Impala. Dean cursed.

In the kitchen with Cain and Crowley, the angel Castiel steeled himself before facing the Father of Murder. He held out his right hand to him and stared resolutely into Cain's eyes. The demon never made a move to take it.

"Why is an angel here? Who are you?"

"My name is Castiel and I'm here to take Dean's place," Cas growled. There was no time, he had to take the Mark _now_.

Cain looked as if he was about to say something when Crowley made a choking noise in the background. He gave the angel a hysterical snort of laughter, "Castiel? What - are you mad?"

His voice grated on Cas' nerves but the angel couldn't afford getting distracted and decided it was best to ignore him- until he remembered, that is. It was Crowley's fault that Dean had the Mark of Cain in the first place. It was his all damn fault that Dean became a demon and their desperate act of taking off the Mark. Castiel's eyes narrowed at him and all he could see was red.

"You!" The angel shot out an arm, pinning the King of Hell in place with his new Grace and squeezing the life out of him. Crowley went down on one knee."If it wasn't for you-"

"Wait," Cain called out, confidently approaching Castiel's form. "Are you worthy, Castiel? Are you a murderer?"

Cas sharply flinched but schooled his expression anyway. He _was_ a murderer. He murdered countless humans. He murdered countless friends. He murdered countless brothers and sisters. Castiel's eyes have gone dark and his hold on Crowley's neck was loosening. But that didn't mean the sniveling demon wasn't quaking in his boots.

"Yes," came the angel's stunted reply.

He closed the gap between him and Cain, entirely freeing the King of Hell from his hold. Crowley took big gulps of air and looked up at the scene before him. The two men grasped each other's forearms, Castiel grunting at the invasion of the Mark, its evil tainting his holy Grace. The curse spiraled bright red under his pale skin then stopped, forming a red angry scar. It was done. The Mark had found it's new master.

Cain spared the King of Hell a measured glance, "I think you should go." With the newly tainted angel trembling slightly in power, anger or both, Crowley surmised that was the best idea. Who knew why the featherbrain wanted to bite his head off but he'd rather take his chances than stay with the madman. "Bollocks," he cursed then disappeared into thin air.

The Father of Murder turned his attention to the angel. "I don't have the First Blade in my possession."

"I know," Cas said, straightening up. "I also know where it is."

Cain furrowed his brows, "I see." However, there was something else bothering him other than an angel taking up the Mark. "There's something different about you. You're much more powerful than a fallen angel... You're not fallen, aren't you?"

Castiel looked at him straight in the eye, "I'm not," he agreed.

Their conversation was suddenly cut short when a loud crash of glass and debris rained on them from a broken window. The swarm of demons were getting more agitated by the minute and Castiel had to take Dean out of there. He looked at Cain knowingly.

"One day, I will call you, Castiel. And you will use the First Blade to end my life. That is the deal."

The angel gave him a brisk nod, and then flew away to where his human friend was currently imprisoned inside his own car. He partly registered the battle cries of many demons as they were given purchase to enter the house. Beams of scarlet light and guttural screams painted the vicinity.

Castiel appeared beside Dean on the passenger's seat and ignored the hunter's bitter scowl. Their conversation had to wait. "Drive, Dean!"

The Winchester grudgingly obeyed, turning his keys into ignition, tires squeaking and crunching down dirt and stones as they sped away from the horror show. Things just got fucked up six ways to Sunday.

"What the hell, Cas?" Dean's voice went up a few octaves high as he drove down the road, speed limits be damned. "What the fuck happened back there? You locked me inside my own car!"

His friend pursed his lips into a thin line before answering, "I saved your ass, Dean. That's what happened."

The hunter was a bit taken aback by the angel's choice of vocabulary. Something was seriously wrong here. Dean carefully inspected Castiel from his grave expression to his rolled up sleeve, the Mark of Cain settling comfortably below the inside of his elbow. The thing already gave the Winchester Goosebumps but seeing it on his angelic friend made it so much more disturbing.

Not to mention how in the world could Castiel teleport - or fly for that matter- if he was as much of a fallen angel like all the other ones on earth? And how exactly did he know where Dean and Crowley were, or their business with the Father of Murder? So many goddamn questions without a single stupid answer.

The frustration was evident on Dean's face but Cas knew this wasn't the right time or place to straight things out. "I'm sorry, Dean," Castiel murmured while closing his eyes. He felt tired. "I can't explain things right now. We need to get to Sam first."

"What? But Sam's-"

"Your childish fight with your brother is nothing compared to this."

Sheesh, someone's acting snappy. Okay, maybe he was a bit concerned with his fight with Sammy but it wasn't fair that Cas would always assume Dean had his head in his ass. He opened his mouth for a sarcastic retort but closed it when he saw the slump of Castiel's shoulders and the haunted look in his eyes. Dean cleared his throat, "Yeah, of course. I know, Cas. It's just... we're in the middle of nowhere and Sammy's probably days away."

The angel blew out a breath then gestured for the hunter to stop driving. Again, Dean didn't argue and obediently pulled the Impala on the side and turned the engine off. He waited for Cas to speak.

Castiel grabbed Dean's right arm and held onto his seat. His human friend quirked a curious eyebrow at him and Cas felt he had to at least forewarn the hunter, "Brace yourself, Dean. We're teleporting to the Bunker."

Dean was just able to suck some air before Baby and its occupants disappeared from Hell's Highway.

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"Oof!" Dean yelped when his head painfully bumped on the roof of the Impala. The car bounced twice on the ground upon arrival, rattling its passengers inside. A heavy cloud of dust surrounded them and tickled the hunter's nose. He sneezed. "The hell, man? Give a guy a better warning!" _Achoo!_ "Dammit."

"My apologies, I'll make sure we land gentler next time," Cas muttered, already getting out and slamming the car door on Dean's offended face. The hunter scrunched up his nose, "'Next time'? There ain't no next time, buddy!" _Achoo!_

Thankfully, the dust was clearing up and the moon overhead provided enough lighting to distinguish the Bunker's entrance. Castiel moved towards the metal door and Dean wasted no time to follow his feathered friend. The angel raised a hand to knock but stopped, looking at the limb like it's the first time he's seen it. He dropped his hand and motioned for the hunter to come closer. Dean didn't want to admit it but this odd behavior with Cas was seriously giving him the heebie-jeebies.

"Cas? What's the hold up?"

There was a flash of guilt on his face but then the emotion was gone in an instant. "Sam's probably resting; I don't want to disturb him. So, hold on."

For the second time that day, the elder Winchester found himself getting teleported somewhere. He realized this would mean he won't be pooping till next week. Dean didn't know what scared him more - that Castiel somehow got his real mojo back and was acting all shifty, or the part where he could zap him anytime, dysfunctional bowels and all?

The said angel groaned in irritation next to him, "You don't have to worry, Dean. You're bowel movement is safe and sound."

"What the - are you reading my mind, Castiel?" The hunter snapped at him. He made sure to put Cas' full name in to make his point home. The featherhead was acting like a dick all of a sudden.

Cas sighed heavily, noticing his mistake. He stared apologetically at Dean, "I'm sorry. It's - it's been a long day." He had been too careless, using his old powers just to feel like a real angel again, even making up a bad lie about Sam. But even with the new Grace pulsing within him, the Mark was steadily creeping under his defenses. He could feel it's darkness. He didn't know if it was pure frustration or the curse was starting to taint his mind. Before his thoughts could stray any further, he felt the weight of Dean's hand on his shoulder. The Winchester had his eyebrows furrowed and wearing a worried frown. Castiel really looked at him then and was surprised to once again see the brightness of his soul.

It's been such a long time since the angel had seen that pureness inside his friend. Maybe taking up the Mark himself gave Dean's soul a chance to remain pure. With that knowledge in mind, Castiel let himself relax and felt very grateful that he took the mission. The world was saved, Dean was saved, and some of their friends were still alive. Like Charlie. Oh how he missed Charlie.

"Dean? What're you doing here?" Sam's sharp tone cut through the silence. He noticed his older brother lurking by the entrance door and another person beside him, hidden a little by the dark. But the silhouette of a trench coat could only mean... "Cas! You friggin' disappeared!" Sam exclaimed, jerking his arms in front of him to convey his concern. Their angelic friend stepped out of Dean's shadow and graced the younger Winchester with a sheepish look.

"I… I brought Dean," Cas said, awkwardly shuffling his hands and pocketing them somewhere in his coat. The older Winchester gave a slight scoff at that.

Sam snorted. Yeah right, as if that little tidbit explained everything. He waved at them to come down. Might as well talk things out while the whole family was there. The two men glanced at each other before going down the stairs single file, Dean purposefully avoiding eye contact with him, and Cas moving sluggishly as if his body weighed a ton. Whatever happened on their little escapade, it looked like nothing good came out of it. And knowing the pair… the hunter sighed. This was going to give him a major headache.

Nobody spoke for a long time after they were all comfortably situated in the library. Maybe 'comfortable' was stretching it a bit thin. Dean sat in his place on the other side, directly facing his little brother, while Cas slumped on his chair between the Winchesters. Sam ignored their depressed sighing.

He clapped his hands in mock cheer, "So. Who wants to go first?" Predictably, no one raised a hand. Though Sam did spot Castiel fidgeting with his shirtsleeve. "Cas?"

"I'm afraid my version is... complicated. It'll take a while," the angel replied, not even lifting his head to look at the younger Winchester. Castiel kept picking at something on his right forearm.

"Okay. Dean?" Sam didn't know if Cas forgot about their plan to track Gadreel with the resonating Grace inside him, or that there was something much bigger that warranted the angel's attention. He seemed stronger too - strong enough to teleport and last time Sam checked, it was something no angel out of Heaven could do. Either way, Castiel was acting very, very suspicious. And things like that never ended well for any of them.

Dean groaned, "You don't wanna know, Sammy. I don't recommend it for bedtime stories." Sam made sure to give him his biggest bitch face.

"Try me."

The older Winchester wearily scrubbed his face. "Fine." To hell with it. No more keeping secrets. "So I was in a bar, okay? Then Crowley was there -"

"Crowley? Dean, you should know better than hang out with demons!" Sam yelled, effectively cutting him off mid-sentence.

Dean yelled back angrily, "I wasn't! Dammit Sammy, just let me finish!" He fixed his brother with a stink-eye before continuing, "He was there and he looked human... ish. I don't know if he's still getting his fix but Crowley seemed non-threatening. Anyway, I was half sober and moping when he started yapping about Abaddon."

"Abaddon?"

Dean shrugged, "Yeah, we didn't really think much about her these days, right?" Sam reluctantly nodded. "So Crowley, being the old gossipy lady that he is, knew something that could kill her. The First Blade..."

The brothers' conversation started to blur to Castiel. Some of their words dissolved to static and background noise. All he could hear, feel and touch in that moment was the Mark, pumping poison and evil into his veins. He was entranced just by looking at it, his fingers delicately tracing the red scar. If the angel could simply just... tune everything out, he could swear the Mark of Cain was singing. Sweet, sweet, melody of blood and death. Castiel could almost taste it on his tongue. Then the peculiar sensation left as fast as it came, leaving the angel disoriented and out of sorts. Cas could still somewhat hear his friends' voices but they were too far away...

Suddenly, there was an explosion of light and sound, his senses all drowned out by a chorus of ghostly whispers and bloodcurdling screams. It was too bright and too loud altogether. He was having a vision.

Castiel watched as familiar but unfamiliar hands soaked in red and foul gore, tearing bodies left and right. Wing prints seared onto the ground, a tall form splayed broken and bloody, green lifeless eyes. Maniacal laughter was echoing and bouncing inside his head. It sounded so much like his voice, enjoying the sick thrill of the hunt. He screamed then, screamed for all he's worth. The Mark of Cain glowed and it grinned at him.

 _"Open your eyes, Castiel. Open them to a whole new world you're about to create. Isn't that what you've always wanted?"_

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 **Ahhh what is that? who is that? too creepy? not graphic enough? ugh please Read/Review/Fav/Follow. See ya next time!**


	3. Come to the Dark Side, We Have Pie!

**A/N: Oh my Chuck! I'm so sorry for updating so long! I had a mild writer's block and a few problems at home but I wrote a long-ass chapter to compensate! please forgive me _**

 **P.S. Anyway, this is an interesting chapter and I'm actually introducing a new Castiel persona called... (SPOILER!) _Darkstiel_.**

 **Disclaimer: Carry on my wayward sooon, there will be peace when you are dooone, Eric Kripke, the WB and CW own Supernaturaaal, so cry some mooore.**

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Chapter Synopsis: _The Winchesters finally learn Castiel's mission and the ugly truth behind the curse of the Mark of Cain. Same song, different verse but who's really playing the tune?_

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 **Chapter 3 – Come to the Dark Side, We Have Pie!**

' **How did I get here?** ' Was his first thought, and then, ' **where am I?** '

Everything was a mesh of distorted color. Wisps of blue and red chasing each other then fading out, some forming the palette of a rainbow, swirling to a slow hurricane. Tendrils of green and yellow lightly reached out to him, teasing, but shied away when he tried to make contact with them. He reveled in this curious world for what seemed like an eternity but then the scene before him slowly changed. There was a black dot in the center of his universe, spiraling ominously towards the bundle of colors. An obsidian hand reached out from the black hole, grasping at anything that passes near it. That Hand was an abomination. He wanted to get rid of it but found that he had no form, no body, to move with. He was just a color, like all the other colors around him.

The Hand finally found its prey, fingertips lightly brushing at an innocent blue wisp. Bright blue gradually turned to dark, then darker, then pure black. It became a thick dark smoke, bumping with other brilliant hues, infecting them with disease and corruption. Soon, everything would be swallowed by the darkness – including himself, but the tainted colors didn't move to consume him. They coalesced together, forming a pitch-black tunnel. There was light at the end of the make-shift tunnel and a person carefully stepped out from it. It seemed like the Hand manifested itself into a familiar face. The entity brushed non-existent lint off its dark pristine suit and looked at him. It regarded Castiel with an interested pair of red eyes. A deep glowing red, like the Mark.

"Like what you see?" It said in a disturbingly familiar growl. "This is what you will become. Not angel, human or demon. Not even god. Just… Darkness." He shivered as he finally realized it was the voice that spoke to him earlier. The entity cocked its head to the side, a mocking rendition of the angel's usual innocent quirk, "You think I'm the Mark of Cain? No, Castiel. I'm your deepest and darkest sin. I'm you." Its mouth morphed into a feral grin, "Welcome to the dark side."

"Cas? Hey! Snap out of it!" Castiel found himself whole and solid again, hands clutching the cold wooden table in the Bunker's library. Dean Winchester hovered above him, an anxious expression on his face. Sam was nowhere to be seen.

"Dean?"

The hunter heaved a lungful of air and expelled it in a rush, "Don't ever do that!" He lifted his hand off Cas' shoulder to snatch a bottle of beer and chug the contents down his throat. The angel swore no one was drinking anything when they sat down to talk. Observing more closely, Castiel counted four empty beers.

"Sam, Cas is back!"

Just like that, the younger Winchester came in bounding and looking harried. He was clutching several books and a Men of Letters folder; he dropped them all unceremoniously as he approached Castiel's sitting form. "Cas? Cas, you okay, man? What happened? You went catatonic for over an hour!"

"What?" Their feathered friend responded lamely, still disoriented and perturbed from his vision - if it could even be called like one. The brothers exchanged worried looks.

Sam eyed the red scar on the angel's forearm, looking stark and blood-like in contrast of Castiel's smooth white skin. He pulled out his chair and sat down heavily, glancing from his friend to his brother, "Dean was just finishing his side of the story when you got all rigid. Eyes glazed over, unmoving. You know, creepy stuff."

"We didn't know what to think at first. Maybe you were, I don't know, meditating? But 15 minutes in and we knew there was some real crap going on," Dean added, sighing. "So Sam and I went to do some research and came up nada." He glanced at the now-empty bottle in his hand, "Or tried to."

Castiel couldn't believe it. He knew it was coming but he was hoping for more time. The Mark of Cain was much powerful than he initially thought. "This isn't supposed to happen... not so soon."

Dean's head jerked up at his words, green eyes scrutinizing the angel's wide-eyed expression, "You know something, Cas?"

Castiel stared mutely at Dean, comparing his healthy features and the blinding brilliance of his soul from the hunter's future counterpart - whom the angel left behind in his old timeline. He remembered the Dean who wore the Mark, obeying the curse's whims. He remembered the Dean who murdered a kid and beaten his best friend to near-death. He remembered the Darkness and its purpose to destroy all of creation. Yes, the angel did know a lot of things. His father made sure of that. Chuck planted every memory, every thing related to them before and after the release of his sister. Some things that he never knew of and never even happened yet. Like Dean's deal with Death and Amara's bond to whoever wore the Mark. Lucifer possessing him. Castiel had to prevent all of those from happening - hopefully, with Sam and Dean's help. Though he prayed they wouldn't just make everything worse and he'd be forced to start from square one.

He turned to Sam. "We might need more drinks if I were to say anything more." Dean raised an amused eyebrow. Cas wasn't kidding.

"Go on, Sammy. Might as well end this nightmare with a bang."

Sam huffed and shook his head, getting up from the table. He went to the kitchen and retrieved three six packs. Might as well.

* * *

In the end, no one except Cas touched their beers. He was already in his third bottle when they decided to start discussing his other side of the story. Looking at his best friend, Dean couldn't shake off the feeling that the angel had changed. He looked better _and_ worse than ever. As if something like that was possible. Castiel seemed confident and gave off a sort of focused atmosphere around him. If Dean was honest with himself, he'd say the Cas during the Apocalypse was back. Just without the stick up his ass... and more human. Though the hunter was glad that somehow Castiel was well and truly back, another goddamn problem just landed in their laps. He saw what the Mark did to his friend and couldn't stop worrying. Judging the fact that Cas was an angel, Dean would've never lasted long with the Mark of Cain on _his_ arm. So he worried. Worried that he dodged the bullet and his best friend jumped the gun.

And knowing Cas, it was more than likely. He's always been a self-sacrificing idiot.

Sam cleared his throat to get both of their attentions, his full concentration directed on Cas' face. "So. The Mark of Cain?"

Dean unconsciously leaned closer, not wanting to miss a single thing. Cas took in a deep breath then clasped his hands together, blue eyes stubbornly trained downwards as if unraveling the mystery of alcohol and oak wood.

"The Mark is a curse. Lucifer originally had it and it didn't do much damage to him, except for bringing forth his genuine hatred for Humanity. Then came Cain, the first murderer. He killed his brother Abel and Lucifer passed the curse to him."

The brothers nodded at every word; they already knew as much. Castiel gritted his teeth before looking up at them. "But Cain was only human. He fell to the Mark's temptation, murdered countless souls for several eons. Nothing could kill him, not even Death himself. Finally, the Mark tainted his soul - bonded with it - and Cain became a Knight of Hell."

"A demon," Sam breathed out and gulped nervously, eyes straining not to look at the Mark. Cas nodded grimly. "Anyone who wears the Mark will go down that road eventually."

Dean abruptly stopped in his tracks, not fully understanding what his friend was saying. "What do you mean 'eventually'?"

Castiel visibly stiffened, pursing his lips and uncertainly flicking his eyes to the hunter's.

"Cas?"

Silence.

"Cas!" Dean said forcefully, almost yelling.

The angel turned his head away from the brothers' calculating gazes, blue eyes squinting at the offending dust on a bookshelf. He knew the older Winchester won't be happy with what he had to say. "The owner of the Mark will never die, Dean. Not truly. Even if the body dies, the person will be resurrected as a demon."

"But why?" The younger Winchester asked before his older brother could spout something inappropriate. Dean looked peeved. Sam shot him with a bitch face.

"Because... the Mark of Cain is a key. It's a key to a lock of the greatest evil."

Castiel gave them a few seconds to let the information sink in, not really knowing if they felt or understood the magnitude of his words. Dean, predictably, was just bullheaded as ever.

"You know what, Cas? I don't really care. I was there first and it should've been me. It's supposed to be my goddamn problem, not yours! So why the fuck did you take my place instead of hauling ass?"

"Dean..." his younger brother whispered harshly, warning him that he was going too far. They knew water was under the bridge, now, but they still didn't see eye to eye yet. Castiel and Dean both ignored him.

Cas growled low and angry, "Because you don't understand, Dean. You didn't understand what you were signing up for. What you could've done if I let you have the Mark-"

"I'm a big boy, Cas. I can handle my own mess!"

Dean knew he was acting like the biggest dick ever but he just couldn't let his best friend get away with all this penance and sacrificing thing without a word or two from him. And also the fact that even now, he still needed Cas to save him. He couldn't force the memories of Cas turning human and getting kicked out of the Bunker away. Just the thought of _Castiel_ helping _him_ rubbed him the wrong way. Maybe that was guilt and ego talking.

He was in Dean's face in a blink, expression thunderous and too blue eyes lightening up with barely restrained Grace. Cas never looked so ethereal and inhuman up close before. The hunter felt a bead of sweat trickle down the back of his neck. Two strong hands pulled at his shirt collar, almost knocking foreheads with the pissed off angel. "You couldn't handle your own mess, Dean," Castiel ground out. "You turned into the very thing we despise and I watched you slowly murder everyone around you. I watched and I couldn't do anything. It was all too late..." he trailed off, shaking Dean a little before dropping his hands and staring at him one more time. Cas broke contact first.

The older Winchester reached out uncertainly to grasp Cas' shoulder. His angelic friend stiffened at the touch but didn't say anything. Castiel's muscles were so wound together; Dean could practically feel the tension in his body.

"Cas? I'm sorry, buddy. I just - I'm worried and pissed you're stuck with that thing on your arm, man. What's really going on?" Dean didn't know what to think about Castiel's outburst. And his earlier fit of temper was just making him extremely guilty. His best friend didn't need anger issues on his already full plate.

Sam watched them carefully, conflicted emotions showing on his face. He was just as confused as Dean was but if what Cas said earlier was put into consideration, then they were all totally screwed. This might just be something that went beyond their pay grade.

"So, um, is there anything we _can_ do about it?" He asked softly after a considerably long silence.

The cap from Cas' fourth beer made a popping sound as he casually twisted it off. He gulped loudly, tipping up the bottle until not a drop of liquid was found. Sam and Dean exchanged another worried look and an impressed one. Castiel distractedly wiped his mouth with the back of his sleeve. "I would warn you to not 'freak out'," he said using air quotes, "but that would just be contradictory."

"It can't be that bad, can it?" Dean muttered.

Sam cast him a sharp glare to shut up, "What're you telling us, Cas?"

"I'm telling you… that I'm the Castiel two years from now. I'm from the future."

The older Winchester's eyes bulged at that. "Holy-"

"-Crap," the younger one supplied.

"It's much worse than you think," Castiel stared at his lap, leaving the brothers in stupefied silence. "God personally sent me here to correct things. Or at least save us all from utter damnation."

"What? Uh, hol – hold on, did you just say _god_ poofed you to two years from your original timeline? The big G-O-D?"

"Yes, and-"

"So Deadbeat Dad finally showed his ass? _That's_ gold. Did he say 'sorry'?"

"Dean, that's not even the point here."

Their feathered friend glared daggers at them, apparently not appreciating their little commentary about his heavenly father. "Exactly. That's not the point. The point is why my father had to send me to this time – to clean up our mess," He glanced at Dean, "Your mess."

The older Winchester shifted uncomfortably in his seat, "Okay, shoot." Dean didn't really want to hear it though. He sensed whatever happened to Cas' timeline was largely a part of his 'punch first, ask questions later' policy. Sam looked like he's about to ask a million questions but held his tongue. Castiel gave them a measuring look before diving in.

"In my timeline, Cain succeeded in giving the Mark to Dean. You two also found the First Blade and killed Abaddon."

Sam stole a glance at his brother with eyebrows raised, then turned to the angel, "But...?"

"But things went downhill after that," Cas sighed. " _Certain events_ led to Metatron uniting the angels and granting them safe passage back to Heaven. Metatron became their hero," he spat the last word, inciting curious looks from Sam and Dean, "and imprisoned me and Gadreel in the dungeons."

"Gadreel? Why was Gadreel with you?" The younger Winchester asked somewhat suspiciously. The last time Gadreel was with any of them, he possessed Sam and killed Kevin under Metatron's orders. Cas was even supposed to help him find the angel with the resonating Grace inside of him until Castiel disappeared, saying something about saving Dean.

Their feathered friend replied, "It seemed he was merely… feeling misunderstood. He wanted to be accepted again; take his honor back, and so I recruited him and he helped me find a doorway through Heaven. We were going to destroy the Angel Tablet but he sacrificed himself on the way."

Dean was skeptical. "You recruited the guy who murdered Kevin and _he_ died for the good cause? Okay, judgments aside, you did destroy it, right?"

"Yes" the angel directly looked into Dean's eyes, voice cracking a bit as he said, "I did. Metatron found me but he was powerless. It was all too late though. I failed, Dean. I failed and I'm so sorry."

"What-?"

"Metatron killed you," Cas whispered brokenly. The Winchesters had to strain their necks to hear anything. "He lured you and he killed you, Dean. Sam was there with you and he had to see you die." He paused, and then took a shaky breath, "I'm sorry Sam, I couldn't protect him." It was the same words – the same apology – he said to Sam after coming back to the Bunker. It fell on deaf ears then, the younger hunter barely noticing him and murmuring the same words over and over again. **Dean's gone. He's not here. Crowley took him.**

Sam didn't know what to say. Dean dying and him being there was actually sickening, but Castiel apologizing to something he couldn't control was heartbreaking. He could only guess what his older brother was feeling at the moment. Dean looked as if he was rooted on the spot, staring at the angel in a mix of complicated emotions. But Cas plowed on, never giving the chance for the brothers to say anything.

"Sam… Sam, he took you home, placed you in your room… He tried to summon Crowley but he didn't show up. Sam didn't have to, actually, because Crowley was already there with you. He knew what would happen if you died, Dean, " Castiel looked down at his clenched fists. "He knew you'd become a demon."

The hunter wanted to puke his guts out. He wanted to puke everything that made up this fucked up situation, wanted to slap the daylights out of Sam for the expression of disgust and horror, and pity and anger on his face. Wanted for Cas to shut the hell up so he could just move on and forget everything that he heard tonight. But he knew the angel had to go on and Dean owed it to him that all those things weren't probably going to happen anymore - what with Castiel having the Mark of Cain instead of him. That fact didn't make anything better. It was just the other way around and Dean really felt like tearing his hair out.

"Was that – ," Dean cleared his throat, "was that the reason why you time traveled?" He glanced at the red Mark on Cas' forearm, "And crashing the party at Cain's?"

"It's part of it but there's more."

"Of course there is," Sam muttered. Dean just wanted this conversation to end. _Now_.

"You disappeared with Crowley and followed him in to Demon Territory. Sam eventually found you and brought you here to cure you with cleansed human blood. We managed to turn you back to human."

Dean thought that wasn't half bad, really. He spoke up, "Uh, well, that's good, right? But what happened with Metatron?" He was genuinely curious but also wanted to sidetrack the angel a bit from his impression of 'The Rise and Fall of Dean Winchester'.

Cas gave him a look but acquiesced. "The angels threw him in jail after his dirty work was revealed. He kept bargaining his release for my original Grace but..." He shrugged, "Yet Metatron came to earth twice. First by interrogation about the Mark and the second, Sam and I," Castiel glanced briefly at Sam, "took him from Heaven through some help and made him human. He led me to the Demon Tablet and what's left of my Grace, and... escaped."

"Dude. A newborn Metadouche slipped through your angelic defenses?"

"Shut up, Dean."

"Bitch."

"Jerk."

The angel was embarrassed to say the least but Sam's bitch face and Dean's offended expression made up for it. He almost smiled at their familiar banter but didn't, only gracing the brothers with an imperceptible quirk of his lips. "Metatron is quite older than me and much more knowledgeable." Cas' eyes darkened as he said, "But he wasn't knowledgeable enough on how to remove the Mark of Cain from its owner." Dean gulped. The talk was back on track.

"We needed to remove the Mark completely. Dean was showing signs of the curse acting up again but we couldn't find anything in the Men of Letters' accounts about it. Though there was something about a spell book called 'The Book of the Damned' that Cha-" Castiel almost slipped. He nervously eyed Sam and Dean's faces, relieved that they didn't catch the name. "that we found. It was an object of evil and abominations but Sam and I agreed to use it." He sighed, "Dean actually refused to use it because it was calling out to him - could feel the bond between the Mark of Cain and the Book."

The older Winchester scrunched his face at his younger brother and turned to Castiel. "Let me guess, you two went behind my back and it turned out to be a bad idea?"

Cas nodded. "Very, very bad. We found a witch, named Rowena - Crowley's mother - to help translate and find a spell to undo the curse using the Book of the Damned."

"Crowley has a mother?" Sam exclaimed. "I-I mean, of course he does, but... a witch? Seriously?"

"I bet she's as double-faced and power-hungry like her son," Dean snorted. "Man, I hate witches."

Castiel cast them a reprimanding look. They were getting distracted. "Yes. Yes she is. But she also succeeded in casting the spell. The Mark of Cain was taken off and Dean was free from becoming a demon again. Though by the doing that, we unknowingly unlocked the most evil entity in the entire universe - the Darkness."

"The Darkness?" Sam parroted.

"Before Light, there was Darkness," recited Cas. His too blue eyes looked far away, "The Darkness is god's sister and her name is Amara. She is destruction and destruction is her purpose. She kept obliterating god's works everytime he created something, so father locked her away - sealed her - for eons so he could make the world. Humans, plants, animals. Life. But she got out..."

Dean was tasting bile in the back of his mouth, "... and here you are." He looked pleadingly at Cas, "But why, Cas? Why couldn't god just take care of her? Why'd you have to come back here and shove yourself at the mess I made?"

"Because there is balance in everything, Dean. Without it, everything would cease to exist."

"Are you saying that if any of them disappears, the universe would too?"

"Yes, Sam. That's why by coming to the past, I had to take Dean's place in possessing the Mark so the balance would still remain. The space-time continuum is also sound. I altered the timeline and erased the older one by conjoining with my past self."

The older Winchester made an interested noise, "And I thought changing things in the past was taboo."

Castiel nodded, "I did too. Until god personally healed me and gave me bigger wings. He sent me here with all the knowledge that happened before and after the release of the Darkness. So I know most of everything that we should and shouldn't do to prevent that kind of catastrophe."

"Huh. That's kind of nice to hear, Cas, but we're worried about the Mark's effects on you. You sure we can't do anything about it? Dean said, chewing his bottom lip.

"Yeah, Cas. Do we even know what the Mark does to an angel?"

"I'm afraid I will... degrade to a darker version of myself, like Lucifer. I won't change quickly, give or take a year, maybe two." He hung his head in silent defeat, "I'm asking for your help here. Sam... Dean. Please, don't do anything reckless to free me from the Mark. I came here to save the world and I'm asking you to help me keep it from harm. If the day comes, _when_ the day comes, I'll leave and you'll never see me again. But remember, I _chose_ this." The angel rubbed the scar on his forearm briefly and nodded at the Winchesters, then disappeared in a flutter of wings.

The brothers didn't even had the time to register the shock of actually seeing an angel poof out of existence while they stared at each other. Each thinking if Cas would be back later or if he's gone for good. Dean was sure he'd be there by morning. The featherhead probably wanted some space and let them process things.

The silence after Castiel's words of promises and goodbyes hung at the Winchesters like the walk to a funeral. Sam was doing his hurt puppy dog face, opening and closing his mouth to say something but losing the nerve to come up with anything. Meanwhile, Dean just kept rubbing at his face, no doubt dying inside and too frustrated to look at anyone's face. His eyes were red-rimmed and faintly burning already. Damn Cas for leaving them to do nothing about it and damn Dean for acting so rash by going to Cain and everything that he did on Cas' original timeline.

Sam and Dean knew no one was sleeping that night. Maybe ever.

* * *

"No, no, no! Someone just messed with the timeline and it's making the Angel Tablet go crazy!" Metatron whined, scrambling from his office chair and holding up the tablet to Gadreel. "See this? It's glowing like a Christmas tree! I need to know who did this, Gadreel. I need to know where they got enough power to time travel."

The angel pursed his lips, looking thoughtful. "Is there a possibility that the Winchesters are behind this?

"Uh, no," Metatron snorted. "But I'm not dumb enough to cross them out. Okay, go on. Check them and report back as soon as possible. If it's not them, this means we've got a new player in town..."

* * *

 **So whatya guys think? I really really really wanna know! Please Read/Review/Fav/Follow. To be continued next time...**


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